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- Materials and methods
1. We examined published studies relating resting oxygen consumption to body mass and temperature in post-larval teleost fish. The resulting database comprised 138 studies of 69 species (representing 28 families and 12 orders) living over a temperature range of c. 40 °C.
2. Resting metabolic rate (Rb; mmol oxygen gas h–1) was related to body mass (M; wet mass, g) by Rb = aMb, where a is a constant and b the scaling exponent. The model was fitted by least squares linear regression after logarithmic transformation of both variables. The mean value of scaling exponent, b, for the 69 individual species was 0·79 (SE 0·11). The general equation for all teleost fish was 1nRb = 0·80(1nM) – 5·43.
3. The relationship between resting oxygen consumption and environmental temperature for a 50-g fish was curvilinear. A typical tropical fish at 30°C requires approximately six times as much oxygen for resting metabolism as does a polar fish at 0°C. This relationship could be fitted by several statistical models, of which the Arrhenius model is probably the most appropriate. The Arrhenius model for the resting metabolism of 69 species of teleost fish, corrected to a standard body mass of 50 g, was 1nRb = 15·7 – 5·02.T–1, where T is absolute temperature (103 × K).
4. The Arrhenius model fitted to all 69 species exhibited a lower thermal sensitivity of resting metabolism (mean Q10 = 1·83 over the range 0–30 °C) than typical within-species acclimation studies (median Q10 = 2·40, n = 14). This suggests that evolutionary adaptation has reduced the overall thermal sensitivity of resting metabolism across species. Analysis of covariance indicated that the relationships between resting metabolic rate and temperature for various taxa (orders) showed similar slopes but significantly different mean rates.
5. Analysis of the data for perciform fish provided no support for metabolic cold adaptation (the hypothesis that polar fish show a resting metabolic rate higher than predicted from the overall rate/temperature relationship established for temperate and tropical species).
6. Taxonomic variation in mean resting metabolic rate showed no relationship to phylogeny, although the robustness of this conclusion is constrained by our limited knowledge of fish evolutionary history.
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- Materials and methods
Faced with the complexity of nature, ecologists have long sought broad patterns as a means of drawing order from variety. One of the most powerful descriptions has proved to be the striking manner in which many aspects of physiology and ecology scale with body size, and a huge body of information has been accumulated on this topic. Most of these data have, however, been concerned with the terrestrial environment. Despite their being by far the most species-rich chordate group (Nelson 1994), relatively little is known of scaling in fish and in his review of scaling relationships in nature, Schmidt-Nielsen (1984, p. 72) bemoaned the lack of any general relationship between metabolic rate and body size in fish. Neither of the detailed compilations by Peters (1983) and Calder (1984) were able to provide any general scaling relationships for metabolic rate in fish.
The metabolic rate of all ectothermic organisms is strongly dependent on temperature, as well as body size. This relationship tends, however, to be clearer in aquatic organisms, where the large thermal mass of water buffers the rate of change of environmental temperature experienced by organisms. The evolutionary signal is thus easier to detect against the noise induced by rapid environmental thermal variability. Although relationships between metabolic rate and environmental temperature have long been established for aquatic (primarily marine) invertebrates (for example, Ivleva 1977, 1980; Ikeda 1985), there have been few summary relationships provided for fish. Even recent text-books and reviews of teleost physiology have based their discussion of metabolic rate and temperature largely on the general picture established over three decades ago by Scholander and colleagues (Scholander et al. 1953).
The relationship between metabolic rate and temperature in teleosts is of particular interest in relation to the polar environment. A now classic experiment by Ege & Krogh (1914) led to the suggestion that the resting metabolic rates of polar fish would be elevated relative to the rates predicted by the extrapolation to polar temperatures of the resting metabolic rate of temperate water species (Krogh 1914, 1916). This concept of metabolic cold adaptation was enormously influential and, although criticized on both experimental (Holeton 1973, 1974) and theoretical grounds (Clarke 1980, 1983, 1991), it has yet to disappear from the literature.
There have, however, been almost no comparative studies of fish metabolism across the ecological temperature spectrum (polar to tropical) since the pioneering work of Scholander et al. (1953). A recent exception was a detailed comparative study of the metabolic rate of six species of sedentary marine fish from tropical, temperate and polar habitats, which demonstrated a curvilinear relationship between resting metabolic rate and temperature (Johnston, Clarke & Ward 1991a). This relationship was similar to that previously found for marine invertebrates and it provided no support for the concept of metabolic cold adaptation.
As an adjunct to this detailed comparative experimental study we have undertaken an analysis of literature data on respiration rate in teleost fish. The aims of this study were to:
1. Derive an overall scaling relationship between metabolic rate and body mass in teleost fish, and to determine any taxonomic variability in this relationship.
2. Derive an overall relationship between resting metabolic rate and temperature for teleost fish, and to determine any taxonomic variability in this relationship.
3. Determine whether this relationship revealed any evidence for metabolic cold adaptation (sensu Krogh).